In recent years violent crimes, crimes of unauthorized entry, and crimes involving damage to real property have increased dramatically. As a consequence, public demand has mounted for burglar alarms and security lighting.
Most conventional burglar alarms require mechanical tripping sensors which must be installed in entrances to the premises. More recently developed systems, such as those shown in the Ott U.S. Pat. No. 3,582,671 and the Stettner U.S. Pat. Nos. 3,713,126, 3,761,912, and 3,764,832, energize building lighting for a short interval in response to audio signals of requisite intensity. Because of their inability to discriminate among audio signals, the systems are effective at times and in environments where background noises and other innocent noises have a sufficiently low intensity to permit their discrimination from the noises of forceable intrusion (typically, pops, clicks, sounds of impacts and sounds of breaking glass, wood or metal). The systems depend on external sources of power, and are, therefore, inoperative during power outages. The need for an alarm system and lighting system is greatest at those times when power outages occur and at those times when authorized persons are on the premises making innocent background noises.
Conventional systems triggered by a low voltage, low power signal source such as a microphone, employ costly high voltage, high power triacs or SCRs triggered by discrete transistors to perform their activation functions. The systems lack versatility in that they are only capable of performing a single switching function in response to the signal of single type of sensor, e.g. the signal from an array of mechanical switches, microphones, etc.
Accordingly, it is a primary object of the present invention to provide an intrusion alarm capable of detecting noises associated with forceable intrusion into physical premises.
Another object of the present invention is to incorporate an emergency lighting system and an audible alarm into an apparatus operative to activate both the lighting system and audible alarm or only the lighting system in response to noises associated with forceable intrusion into the physical premises, and operative to provide emergency lighting during power outages.
Yet another object of the present invention is to provide an audio detection apparatus capable of differentiating between normal background noises such as aircraft and traffic sounds, i.e., noises with waveforms having slow rise times, and noises associated with forceable intrusion such as clicks, pops, and sounds of impacts, shattering glass, etc. i.e., noises with waveforms having high amplitudes, fast rise times and frequencies in the mid-audio range.
A further object of the present invention is to provide a sound activated alarm system having a monostable or one-shot multivibrator delay circuit and variable resistance elements which may be employed to select the duration of activation of an audible alarm in response to noise and which may be employed to provide a preselected exit delay to permit an operator to arm the system and leave the premises without activating the alarm.
A further object of the present invention is to provide an inexpensive fabricated intrusion alarm including integrated circuit inverters utilized for audio signal filtering and amplification.
Yet a further object of the present invention is to provide an inexpensively fabricated intrusion alarm having selectable exit delay and alarm duration controls incorporated into a circuit employing logic gates as its active elements.
These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the appended drawings.